The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.
A transfer chute can be described as any static interface between two conveyor belts or between a piece of operating equipment (such as a screen or crusher) and a conveyor belt. Transfer chutes are an integral part of a conveyor system and such systems are commonly used and relied upon in the bulk materials handling industry.
Transfer chutes, particularly in industries that are handling abrasive ores or ores that could be described as complex due to their variability in size, moisture content and material shape, are a major burden to maintenance. They can also be a major constraint to production if they do not have the capacity of the conveyor system in which they operate and through the maintenance needs that require scheduled and un-scheduled maintenance.
Accordingly, there is a need for a transfer chute for which maintenance requirements and consequences are minimised or at least reduced. Indeed, issues associates with transfers chutes are considered to be a major constraint to production in bulk materials handling industry.
The design of transfer chutes is a fundamental issue in meeting such a need.
It is now accepted that the key design criterion has always been:                (a) The transfer chute must be able to handle the capacity of the conveyor or component that feeds bulk material into it; in other words it should not be a constraint to the system capacity.        (b) The transfer chute should not through its design create uncontrolled build-up of material that could create a flow constraint or blockage.        (c) The transfer chute should present the bulk material flow onto the receiving conveyor belt (or receiving component) with the minimum of dust and spillage and in a manner that does not in itself cause problems with the operation of the rest of the system, for instance by causing the receiving conveyor belt to track off.        (d) The transfer chute should preferably be of a design that minimised the need for maintenance as maintenance downtime will limit plant capacity over time.        (e) Maintenance functions on the transfer chute, where necessary, should preferably be facilitated.        
These design ideals have been long recognised as the guiding principles in the design of any transfer chute. Modern transfer chute design can arguably be dated to the development in the late 1980's of what is commonly termed the “Hood and Spoon” transfer chute in Gladstone Queensland. The development was driven by the need for much higher capacity transfers than was traditionally used in the coal industry as we were starting to run conveyor belts much faster and using much wider belts. Further there was a capital cost penalty in going to very wide conveyors so developing transfers that could handle higher material volumes when the belts were running much faster had significant capital cost implications.
The “Hood and Spoon” transfer chute designs were developed by applying the principles of fluid flow to solid materials, along with friction assumptions based on the Coulomb friction model. In applying these principles to transfer chute design, a number of issues were raised, including:                (a) The accurate calculation of the material flow trajectory off the head pulley of the belt of the discharge belt conveyor. There were many published papers on the subject that are referenced in the publication “The Transfer Chute Design Manual for Conveyor Belt Systemsi” (see www.conveyorsystemstechnology.com) written primarily by the present inventor, Colin Benjamin.        (b) The accuracy of the flow models developed using these principles given the importance of flow control in transfer chute design        (c) How to manage the high material speeds and the consequent high wear encountered on the wear liners (this was solved for coal by the use of ceramics but proved a much more difficult problem for more abrasive ores)        
Using fluid flow principles and the Coulomb friction model for sized washed coal did create reliable transfer chute designs which led to many attempts to utilise “Hood and Spoon” transfer chutes for broader applications with questionable outcomes. This in turn created new areas for active research with particular emphasis on material flow properties and the simulation of them using DEM (Discrete Element Method) as a means of identify areas of high pressure (and therefore higher abrasion or potential flow constraints or both). It also led to variations in transfer chute design and in particular the development of what is known as the WEBA Chute that used a ledge design to create more of an ore-on-ore flow within the transfer chute by allowing the ore to overflow from ledge to ledge, thus minimising abrasive wear as an issue and thus extending the mean time between maintenance considerably.
Separately, the inventor along with colleagues continued on research transfer chute design. The design issues encountered particular problems including:                (a) Identifying that the trajectory models being used were not accurate. Through sponsored research and reverse engineering over many years, Dr. Shams Huque and Colin Benjamin developed a very accurate calculation that can be now be applied universally to all materials.        (b) Identifying that complex ores and those containing a diverse range of particle sizes, variable moisture content and cohesive or adhesive ores could not be easily evaluated for their flow properties using any known techniques. It was the pioneering work done by Peter Donecker (see Donecker P. Dynamic Scale Modeling (DSM) of transfer chutes—Australian Bulk handling Review, Sep./Oct. 2011) wherein he developed scale modeling techniques based on the scaling principles of Froude and then extended them to cohesive ores that opened up a methodology of accurately assessing complex material flow.        (c) Identifying very early that flow in most transfer chutes was very different from the flow encountered in bins and hoppers. The significance of the difference between the two flow regimes is well summarized in a paper “On Dense Granular Flow” by G. D. R. Midi (see Eur.Phys.J.E, 14, 341-365). It characterizes various flow regimes and clearly distinguishes between the flow regime in bins and hoppers and transfer chutes. In bins and hoppers where flow is not continuous, the flow is described as quasi-static flow. Such flow is also evident in some transfer chutes such as rock box type transfers, cascade or overflow transfers such as the “WEBA” chute or transfers that have had small ledges installed to “manage” wear. Flow within transfers where the flow is continuous is described as dense granular flow. The present invention relates to such a continuous flow transfer and as such will be described herein as dense granular flow. The previously mentioned publication is important as it has 100 additional references on this subject and therefore represents a body of research that illustrates the complexity of solid flow through transfer chutes. This publication confines its work to materials that are not cohesive, acknowledging that such materials represented even more complex issues that were beyond current research.        (d) Identifying very early that the material properties of ores could not be scaled. In other words, it was not possible to take a sample of the material being processed and attribute physical properties to it for use in transfer chute design by re-sizing the material, as was often done by others as part of an assessment of the ore characteristics.        
The present invention can be applied generally to all types of transfer applications but was specifically developed to manage the complex ores that are encountered in many hard rock applications. The term “complex ores” as used herein refers to ores having any or all of the following characteristics:                (a) Large material size variations.        (b) Variations in moisture content that will create flow variations that must be managed within the transfer chute in order to avoid build-up and blockages.        (c) High volumes of micro fines (−200 micron material) or ultra-fines (−20 micron) that could agglomerate with moisture and thus create cohesive, or worse adhesive, mixtures that could create build-up or blockages within the transfer chute. Conversely these same particles could create dust issues in the absence of moisture.        (d) Highly abrasive ores in general as they create maintenance issues that must be managed.        (e) Lump sizes greater that 150 mm.        (f) Material containing cohesive or adhesive contaminants.        
Logically, the most difficult ore types have all of these characteristics.
It is against this background that the present invention has been developed.